when designing a lens, caracteristics are put in a level to valance a design (a way to say it)

so what most be sacrifice in order to gain sharpness.

-- r watson (al1231234@hotmail.com), July 27, 2001

Answers

I think the distinction of sharpness in modern optics is really limited to the discussion of edge-to-edge sharpness. The advances in the inplementation of aspherical surfaces (especially with the Leica lenses) has really done wonders for corner to corner sharpness and lower levels of light falloff at maximum aperture. I think what gets sacrificed is the subjective term "bokeh".

To get the kind of sharpness from the newer 35 Cron Leica had to correct more for spherical abberations (hence the aspherical surface) and when spherical abberation is neutral to over-corrected the "bokeh" suffers. This is why in my humble opinion the older 35 Cron and the 35 Lux ASPH have a more pleasing "bokeh" (both are sharpest in the center and taper off at the edges) than the newer 35 Cron or 28 Cron (which are uniformally sharp across the field).

Of course this is all subjective and one can also argue for the bokeh of the newer lenses but "to each his own".

Then again, one can also point to the Nikkor lenses which are over- corrected for spherical aberrations and aren't really designed with "bokeh" in mind. That is what you pay for in Leica glass. Somehow, Leica is able to design their ASPH surfaces so that they approach total correction of spherical aberrations on the low side. So there's always a touch of residual spherical abberation in the glass to give the pleasing OOF effects (as witnessed by the 24 Elmarit... an outstanding lens in my arsenal). But for the 35 mm focal length I felt that Leica's approach to perfection was an exercise in compromise.

Cheers,

-- John (ouroboros_2001@yahoo.com), July 28, 2001.

Field curvature

-- martin tai (martin.tai@capcanada.com), July 28, 2001.

I have never heard of bokeh being an aberration and I am doubtful that designers actually consider it as a characteristic of a lens. If anyone has data to prove otherwise, I'd like to hear it. BTW, spherical aberration can be corrected out nearly as well with spherical surfaces as with aspherics by traditional means such as using super high index glass and lens bending.

-- Steve Rasmussen (srasmuss@flash.net), July 28, 2001.

Lens bending? So Leica has flexible glass now? What'll they think of next? Bokeh isn't an abberation of course. But it's a characteristic Leica must have been aware of for many years. The good bokeh of so many Leica lenses over the years can't be a coincidence. Surely it has been intentional.

-- Bob Fleischman (RFXMAIL@prodigy.net), July 29, 2001.

Bob, your are right.

The design of lens is much an art as science. It is not possible to correct all and every high order abberations, hence, the the blend of residue abberations makes up the characteristics of Leica lenses.

Just like different brands of wine, has different taste and favour even though the main components are water and alcohol.

Like violins, the sound of an Antonio Stradivarius is differernt from Nicolo Amati.

The lens designers of Wetzlar, Midland and Solms are the equivalent of masters of Cremona

-- martin tai (martin.tai@capcanada.com), July 29, 2001.

What must be sacrificed in order to gain sharpness?

Mostly, your bank account balance.

-- rob (rob@robertappleby.com), July 29, 2001.

Wade through Erwin Put's various treatise (links below) and you'll know a lot more and probably be more confused in the process. At least Erwin clears up a lot of misconceptions.

http://www.imx.nl/photosite/leica/technics/optics01/lensdesign01.html

http://www.imx.nl/photosite/leica/magazine/threegen.html

http://www.imx.nl/photosite/leica/technics/faq.html

-- Bud (budcook@attglobal.net), July 29, 2001.

Bob: Lens bending is a very real technique used by designers to help correct coma and spherical aberration. Maybe Martin will explain it to you.

-- Steve Rasmussen (srasmuss@flash.net), July 29, 2001.

One thing that I have heard is that highly corrected Leica lenses can suffer from some slight vignetting at wide aperture, although this can be overcome by stopping down by one or two f-stops.

-- Ray Moth (ray_moth@yahoo.com), August 01, 2001.

I also belive vignetting can be easily corrected in printing than an aberation.

-- r watson (al1231234@hotmail.com), August 01, 2001.

The cult of sharpness came about, I believe, because of the needs of commercial photographers to have snappy, contrasty, razor sharp images. But there is much more to the character of a lens than sharpness, which is why many photographers--especially the ones who have recovered from the "latest is greatest" fever--prefer older lenses. But, as I have said elsewhere, trying to discuss the character of a lens with most photographers would be like trying to discuss the character of acoustic pianos with pop keyboard players. The nuances have long been lost in the noise.

-- Peter Hughes (ravenart@pacbell.net), August 01, 2001.

I'm waiting to hear how lens bending works. Can this be done at home?

-- Bob Fleischman (RFXMAIL@prodigy.net), August 02, 2001.

Well, my wife once discovered a 135/3.4 I hadn't told her about. When she was through, the lens barrel had acquired a substantial curvature. Maybe that's what this was about. Fortunately I had full passport coverage, because I needed it to go and live in another country till she cooled down...

-- Paul Chefurka (paul_chefurka@pmc-sierra.com), August 02, 2001.

Donīt let cool down too much Paul, remember the temperature of color. Keep it 3.4...

-- r watson (al1231234@hotmail.com), August 02, 2001.

OK Bob: It was discovered many years ago that a lens element had more spherical aberration when both surfaces had the same radius of curvature as opposed to having different curvatures. Designers found that a ratio in curvature between the two sides of around 6 to 1 nearly eliminated spherical. This bending of the lens away from a symmetrical shape is known as lens bending. No, they don't actually bend the lens, it is ground to the designed shape.

-- Steve Rasmussen (srasmuss@flash.net), August 02, 2001.

Well Steve, lens designing can be as fascinating as making pictures. I confess my self as a frustrated mathematic.

-- r watson (al1231234@hotmail.com), August 02, 2001.

Some bokeh stuff I found recently:

Tamron 90/2.8 bokeh pictures. I like my 90/2.5 bokeh a bit better I think, although I dont think the pics on this link were taken wide open: http://www.geocities.com/SoHo/Workshop/8827/TamronBokeh.html

Links: http://www.kenrockwell.com/tech/bokeh.htm http://www.imx.nl/photosite/leica/technics/optics01/lensdesign01.html http://www.imx.nl/photosite/leica/technics/faq.html http://www.imx.nl/photosite/leica/magazine/threegen.html http://www.canon.com/do-info/ http://www.foto.no/nikon/lens_surv.html http://nemeng.com/leica/

"Bokeh" by Peter Zimmerman. http://www.slonet.org/~dkrehbie/bokeh/bokeh.htm

A Technical View of Bokeh: http://fox.nstn.ca/~hmmerk/HMArtls.html#anchor26001 http://fox.nstn.ca/~hmmerk/HMBooks.pdf http://fox.nstn.ca/~hmmerk/DOFR.html http://fox.nstn.ca/~hmmerk/

Minox Historical Society: Bokeh: http://www.minox.org/bokeh.html

Bokeh-Shmokeh? http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=005rYD

Bokeh: Various Questions: http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000fFO

Le*ca Test vs Trial part 2 and Re [Le*ca] Diffraction limited; bo-ke: http://mejac.palo-alto.ca.us/leica-users/v18/msg09754.html http://mejac.palo-alto.ca.us/leica-users/v17/msg11954.html

Re: "If it ain't bokeh, don't fix it!" or "So Confused I'm going in Circles. http://www.lynnfarmerphoto.net/35MMBoard/messages/2dqtr99/3896.html

Other messages: http://www.lynnfarmerphoto.net/35MMBoard/messages/3dqtr99/5343.html http://digistar.com/rollei/1999-09/0629.html

*YAWN* Time for bed, methinks. More pictures to take tomorrow!

Dave Bellamy.

-- David Bellamy (dbellamy2k@aol.com), August 25, 2001.

Some pretty good stuff on those links Bud, - better than most I have found on the web. I was looking for some good lens design information, or some things referring to camera lens 'quality', resolution, MTF?, SQF?, bokeh etc. Any more ideas for websites or books on those?

I was particularly fascinated by how the designers manage to get the out of focus image to be 'centre-weighted' on both sides of focus, giving good bokeh, or if that is indeed possible - it seems to be according to some things I have read lately.

It is good to know that some designers at least consider the aesthetics of the image as well as the technical issues such as sharpness of resolution.

Kind regards,

Dave Bellamy.

-- David Bellamy (dbellamy2k@aol.com), August 25, 2001.

I think the best "BOKEH", is the adjustable kind. Sometimes, I also like some auto focus, and maybe I'll have about 6 frames a second. Oh, you'll need a Nikon 105, or 135 F2 DC to adjust your "BOKEH". Leica does'nt make one. What am I thinking? No one else does either!!

-- Brian Harvey (bharvey423@yahoo.com), September 29, 2001.

Here someone has attempted to simulate bokeh with a rendering program. I wonder how it compares to the real thing.

Simulated Bokeh Rendering

-- Peter Hughes (ravenart@pacbell.net), September 30, 2001.